The present invention relates to magnetic flux sensors, more particularly to magnetic flux sensors suitable for sensing magnetic flux through relatively large areas.
There currently exists no practical method to measure the total static and dynamic magnetic flux passing normally through a large area. Semiconductor Hall devices are commonly used in magnetic machines, but they are small and essentially sample a single point. Magnetoresistive devices are becoming more practical; however, they are small and they sense flux down the device axis and not though the sensor thickness.
Many devices would benefit from a large area magnetic flux sensor. For example, an electrodynamic actuator produces forces proportional to the current through the coil conductors and the total flux perpendicular to the coil surface. Typically the coil is designed to be wider than optimum to keep the flux within the area of the coil as it moves, and to thereby reduce force dependence on position. If the total flux perpendicular to the entire coil surface were known, then the conductor current could be controlled to eliminate the force dependence on position. This would allow the coil width to be optimized for more efficient actuator operation.
U.S. Pat. No. 6,975,109 to Bo Su Chen discloses a microelectronic sensor that uses the Lorentz force and a piezoelectric effect to measure magnetic flux. A direct current is passed through a first layer, and the resulting Lorentz force causes shear in a piezoelectric second layer, which produces a voltage proportional to the magnetic flux. It should be appreciated that the device disclosed by Chen is not capable of continuously measuring a static or slowly varying magnetic flux. A statically induced piezoelectric voltage will dissipate with time, and stray electrical charge noise will build up in the detection circuit and degrade the flux measurement accuracy of Chen's device. Also, the construction methods of the apparatus disclosed by Chen limits its use to a small area. Finally, Chen's device will have a low sensitivity, because piezoelectric materials have a greatly reduced voltage response to shear as compared to extension modes.